Three-way valves have many industrial uses and are common in all kinds of assemblies. Most three-way valves are ball valves, manually operated in most cases. In order to operate such valves automatically, an electric or hydraulic motor, or an actuator, must be mounted on the ball valve to shift the interconnection and communication between the valve passages. Actuators and electric motors are both unwieldy, expensive and complex. In addition, ball valves also suffer from a fundamental shortcoming, in that their sealing is achieved by a close fit between the ball surface and the surface of a rigid seat mounted on the valve body. The relatively large friction area is sensitive to entrapped sand or other particles, causing the valve to seize and interfere with the operation of changing the state of communication between the valve passages.